Harvesting of kelp requires serious attention

 

Another Life: A towering lorryload of wrack at the Leenane cross-roads the other morning was a reminder of one of Connemara's traditional occupations once the summer visitors have gone.

Like the sheltered maze of inlets along Galway Bay, the inner reaches of Killary Harbour are thick with Ascophyllum nodosum, the knotted wrack of rocky shores (the Killary sheep go down to graze it, adding a special quality to their meat) and its harvesting contributes to an industry worth €1 million a year to the economy.

On the outer Atlantic coast, a quite different family of seaweeds - the tough, long-bladed kelps - are part of a declining harvest, as hand-gathering of "sea rods", washed in by storms, is virtually at an end.

But kelp's value to the alginate industry is as great as ever, and harvesting by machine, both of kelp and wrack, is among the more pressing proposals for marine development.

In Norway, for example, the offshore kelp forest is harvested by 15 specially designed seaweed trawlers, using dredges to haul up each year some 180,000 tonnes of Laminaria hyperborea, the broad-fingered kelp of deeper water. French harvesters use machines called "scoubidous" to twist around and pull up the shallower Laminaria digitata - 10kg at a time in 30 seconds.

The Marine Institute sees harvesting in Ireland as worth €30 million by 2020, but only if such machines are brought into play. It will work on a regulatory framework and management plan for "sustainable, scientifically-based harvesting" - this in agreement with other agencies, among them the National Parks and Wildlife Service (NPWS).

Among the Special Areas of Conservation, designated by the NPWS for Europe's Natura network, are 36 marine ones with reef habitats, such as those at Achill Head and the Aran Islands, and many more where the offshore kelp forest is important to ecosystems of bays or estuaries. It commissioned five experts to review kelp's significance to ocean life.

Their sources ranged from Chile to California, Tasmania to South Africa, eastern Canada to Norway. But Irish conditions are distinctive, with a warmer Atlantic coast and a more diverse marine life than in more northern countries. We need our own research - a lot of it - before we start licensing mechanical harvesting.

The experts' report, edited by NPWS marine ecologist Dr Eamonn Kelly, already concludes that even well-managed harvesting puts too much pressure on natural kelp beds to be permitted in Natura sites. In other areas, it says, "Well-managed and controlled kelp harvesting could be envisaged, but experience to date in the Irish inshore zone gives no grounds for optimism that 'owned in common' resources can be managed rather than over exploited and then abandoned." The shelter, nursery nooks and protection from predators that kelp forests offer marine flora and fauna are well-known. But some of the most interesting research explores kelp's "primary production". This, rather like the rain-forests ashore, is among the highest known in aquatic ecosystems and far more intense even than the explosive abundance of phytoplankton. A review for the Marine Institute also stresses the "high ecological significance" of kelp forests and urges that their management for machine harvesting should "pursue a precautionary approach".

Every year, using photosynthesis, the kelp plant grows a whole new blade, while its "stipe" or stem gets bigger. But very little of this growth is grazed directly. It nourishes the food chain mainly as detritus - particles worn from the blade tip, or broken down in annual decay, or when the plant is uprooted by storms. Up to 60 per cent of the carbon in coastal invertebrates - molluscs, worms, etc - can be traced to kelp photosynthesis.

Even the mucus that keeps kelp slippery (to reduce the damage from wave action) enriches the inshore food chain, through its reproductive spores (6 billion a year from Laminaria digitata) and its dissolved carbon. And this enrichment doesn't stop at lobsters, fish or even dolphins. Kelp helps seabirds, marine ducks and divers by offering shelter for underwater foraging. Drifting ashore, its detritus nourishes the organisms of sandy shores, otherwise often bare and low in nutrients, and so provides food for flocks of wading birds. Winter's drifts of washed-in kelp, with their little crabs, sandhoppers and kelp-fly larvae, offer more rich foraging to species such as turnstones and oystercatchers.

The Role of Kelp in the Marine Environment is available at www.npws.ie/ PublicationsLiterature/IrishWildlifeManuals/ For a closer look at seaweeds of all kinds go to www.seaweed.ie